This invention relates to processes separating 1,3-propanediol, glycerol, or a mixture of 1,3-propanediol and glycerol from biological mixtures using a molecular sieve.
1,3-Propanediol is a key monomer ingredient for polytrimethylene terephthalate (3GT), a high-performance polyester with a variety of applications in apparel, carpet, etc. The cost of 1,3-propanediol synthesis and separation plays a critical role in the total cost of the 3GT polyester.
Various routes to produce 1,3-propanediol are found in the literature. These routes include commercially practiced chemical synthesis routes (e.g., acrolein hydration and subsequent hydrogenation), and an uncommercialized biological route (e.g., from glucose through glycerol to 1,3-propanediol). In either case, the synthesis of 1,3-propanediol results in impurities which must be removed before polymerization. For the acrolein route, these impurities include water, acrolein, and other organic compounds. Similarly, the biological route from glucose can have impurities such as water, glucose, organic acids, salts, glycerol, and other compounds. Given the high boiling point and hydrophilicity of 1,3-propanediol, economic separation of 1,3-propanediol from these contaminants and from reaction by-products and/or reaction co-products by standard means is difficult.
Known processes to purify 1,3-propanediol have serious limitations. Liquid-liquid extraction of aqueous 1,3-propanediol (Malinowski, Biotech. Prog. 13(2), 127-30 (1999)) was disclosed as xe2x80x9cnot good enough to make simple extraction efficientxe2x80x9d. Another liquidxe2x80x94liquid extraction (DE 86-3632397) uses cyclohexane to extract dimeric acrolein from 1,3-propanediol; however, the process takes longer than 1 hour and is of little use for removing impurities other than acrolein. HPLC separations of 1,3-propanediol (Mao et al. J Liq. Chromatogr. 17(8), 1811-9 (1994)) with ion-exclusion or reverse phase methods are well known but can be used only at small scale because of the cost of chromatographic media and high pressure operation. One standard technique to purify the 1,3-propanediol includes evaporation of the process stream followed by distillation, both of which require extensive quantities of heat input and can be costly.
In addition, it is well known that processes to produce 1,3-propanediol can suffer feedback inhibition; that is, particularly for the biological route, the production of high concentrations of 1,3-propanediol can decrease the rate of additional 1,3-propanediol production or cell growth (Cameron et al. Biotech. Prog. 14, 116-25 (1998)). Thus, there would be additional value for a separation method capable of use in situ during 1,3-propanediol production.
Selective sorbents such as carbons and zeolites have been proposed for 1,3-propanediol separation. The effectiveness of separation using such sorbents varies with the components of the biological mixture and the sorbents involved. The successful design of sorbent-based systems is considered an important factor in the separation process.
Zeolites can be generically described as complex aluminosilicates characterized by a three-dimensional framework structure enclosing cavities occupied by ions and water molecules, all of which can move with significant freedom within the zeolite matrix. In commercially useful zeolites, the water molecules can be removed from or replaced within the framework without destroying its structure. Zeolites can be represented by the following formula: M2/nO.Al2O3.xSiO2.yH2, wherein M is a cation of valence n, x greater than 2, and y is a number determined by the porosity and the hydration state of the zeolite, generally from 0 to 8. In naturally-occurring zeolites, M is principally represented by Na, Ca, K, Mg and Ba in proportions usually reflecting their approximate geochemical abundance. The cations M are loosely bound to the structure and can frequently be completely or partially replaced with other cations by conventional ion exchange.
The zeolite structure consists of corner-linked tetrahedra with Al or Si atoms at centers of tetrahedra and oxygen atoms at comers. Such tetrahedra are combined in a well-defined repeating structure comprising various combinations of 4-, 6-, 8-, 10-, and 12-membered rings. The resulting framework consists of regular channels and cages, which impart a useful pore structure for separation. Pore dimensions are determined by the geometry of the aluminosilicate tetrahedra forming the zeolite channels or cages, with nominal openings of 0.26 nm for 6-rings, 0.40 nm for 8-rings, and 0.55 nm for 10-rings and 0.74 nm for 12-rings (these numbers assume ionic radii for oxygen). Those skilled in the art will recognize that zeolite with the largest pores being 8-rings, 10-rings, and 12-rings are considered small, medium, and large pore zeolites, respectively. Pore dimensions are critical to the performance of these materials in catalytic and separation applications, since this characteristic determines whether reactant/adsorbent molecules can enter and product molecules (in the catalytic application case) can exit the zeolite framework. In practice, it has been observed that very slight decreases in ring dimensions can effectively hinder or block movement of particular reactants/adsorbent or catalysis products within a zeolite structure.
The pore dimensions which control access to the interior of the zeolite are determined not only by the tetrahedra forming the pore opening, but also by the presence or absence of ions in or near the pore. In the case of zeolite A, for example, access can be restricted by monovalent ions, such as Na+ or K+, which are situated in or near 8-ring openings as well as 6-ring openings. Access is enhanced by divalent ions, such as Ca2+, which are situated only in or near 6-rings. Thus, KA and NaA exhibit effective pore openings of about 0.3 nm and 0.4 nm respectively, whereas CaA has an effective pore opening of 0.5 nm.
Molecular sieves, of which zeolites are a sub-class, have recently been considered for 1,3-propanediol purification. The zeolites used for 1,3-propanediol purification were not of the proton form and therefore were susceptible to contamination of the mixture or adsorbate through leaching of the cation. Guenzel et al. (Chem.-Ing-Tech. 62(9), 748-50 (1990)) examined de-aluminized NaY and silicalite for separation of 1,3-propanediol/water solutions; they obtained a maximum loading of 0.12 g 1,3-propanediol/g zeolite. However, they did not investigate glycerol selectivity. Schlieker et al. (Chem. -Ing. -Tech. 64(8), 727-8 (1992)) used activated carbon, but experienced significant non-specific adsorption of the costly intermediate glycerol and achieved 1,3-propanediol fermentation productivities of only 2.5 g/L hr. Schoellner et al. (J. Prakt. Chem. 336(5), 404-7 (1994)) examined two X, two Y, and a Na-ZSM-5 zeolite. The Na-ZSM-5 was found superior to the X and Y zeolites, but again can leach a salt into the mixture or adsorbate stream. The recovery of 1,3-propanediol from the zeolite was not discussed.
Silicalite has been used for ethanol recovery from dilute aqueous solutions. In one implementation (Sano et al. J Membr. Sci. 95(3), 221-8 (1994)), silicalite membranes on a stainless steel or alumina support were used as in a pervaporation method to obtain selectivity of greater than 60 for ethanol to water.
Additionally, H-ZSM-5 zeolites have been used as a separation tool of leucine and isoleucine from aqueous solutions (EP 645371). H-ZSM-5 (Si/Al=14) was used to separate isoleucine from leucine in an aqueous mixture, and then the zeolite was regenerated by contact with base, a process which generates waste salts which must be disposed or treated with expensive electrodialysis. Leucine and isoleucine, both six carbon moieties with bulky amine and acid groups, have much greater molecular size than 1,3-propanediol, which has only three carbons. Yonsel, S. et al. reported very low loading of the desired adsorbate, leucine, amounting to less than 0.04 g leucine/g zeolite. Adsorption and desorption of ethanol from zeolites by temperature variation is known in the art, but the case of desorbing a zeolite-adsorbed product with ethanol was not well known. In JP 01153058, separation of flavors from fermentation products is performed by adsorption with zeolites and desorption with ethanol but these products have distinctly different hydrophobicities and structures and thus such a method is not obviously applicable here.
Improvement in processes for purifying 1,3-propanediol, glycerol, or a mixture of 1,3-propanediol and glycerol from fermentation broth, particularly with respect to product recovery, energy consumption, and feedback inhibition, are needed. A technique which would selectively remove the 1,3-propanediol during the fermentation reaction would be of tremendous utility. Such a technique would be expected to decrease the available 1,3-propanediol concentration, thereby removing feedback inhibition and increasing the total production rate of 1,3-propanediol. As a result, higher capital productivity and potentially higher reaction yields would be achieved.
Applicants provide a process for separating material from a mixture comprising the steps of: (a) contacting a biological mixture containing 1,3-propanediol, glycerol, or 1,3-propanediol and glycerol with a sufficient amount of a zeolite selected from the group consisting of MFI, MEL, BEA, MOR, FAU, LTL, GME, FER, MAZ, OFF, AFI, AEL, and AET and materials of the same topology as these zeolites; (b) contacting the zeolite of step (a) with a desorbant such as an ethanol:water solution or any C1-C4 alcohol:water solution; (c) collecting the 1,3-propanediol, glycerol, or mixture of 1,3-propanediol and glycerol eluted from the zeolite in step (b); and (d) optionally repeating the series of steps (a) through (c) at least one time. Additionally, the process includes selecting in step (a) a first zeolite to selectively adsorb a mixture of 1,3-propanediol and glycerol from the biological mixture, and after performing the series of steps (b), (c), and optionally (d), then performing step (a)xe2x80x2 by contacting the mixture of 1,3-propanediol and glycerol with a second zeolite to selectively adsorb 1,3-propanediol or glycerol from the mixture of 1,3-propanediol and glycerol, (b)xe2x80x2 contacting the zeolite of step (a)xe2x80x2 with a desorbant such as an ethanol:water solution or any C1-C4 alcohol:water solution; (c)xe2x80x2 collecting the 1,3-propanediol or glycerol eluted from the molecular sieve in step (b)xe2x80x2; and (d)xe2x80x2 optionally repeating the series of steps (a)xe2x80x2 through (c)xe2x80x2 at least one time to obtain a purified 1,3-propanediol or glycerol.